The MRI apparatus is an apparatus that measures an NMR signal generated by spin of nuclei composing an object, in particular human body tissues, and images forms and the like of the head, abdomen, extremities, etc. two-dimensionally or three-dimensionally. A thermal noise caused by irregular motions of electrons in an electronic circuit is included in the NMR signal measured by the MRI apparatus. Therefore, noises are superimposed in the acquired image, which reduces an SN ratio of the image.
As a method to solve this problem, filtering can be recommended. Because filtering is a post-process to be performed after measurement, there is an advantage that it does not accompany measurement time extension. However, noises as well as required signal information are lost in a linear filter, and this results in a problem such as a blurred image, i.e. resolution reduction.
In order to avoid this, the filtering method that prevents the loss of the required information included in an image is suggested, and there is the following method as an example. The method holds the structure of the image by changing a weighting function shape of the filter based on the result after detecting directionality of a target pixel and the surrounding texture or detecting a structure of an edge or the like (for example, see Non-patent Literature 1). At this time, the detection of the directionality and the structure is performed on the basis of a pixel value of the image.